<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="https://cdn.staticfile.org/react/16.4.0/umd/react.development.js"></script> 
    <script src="https://cdn.staticfile.org/react-dom/16.4.0/umd/react-dom.development.js"></script>
    <script src="https://cdn.staticfile.org/babel-standalone/6.26.0/babel.min.js"></script>
</head>
<body>
    <div id="app"></div>

    <script type="text/babel">
       function tick() {
        const el = (
            <div>
            <h1>Hello, world!</h1>
            <h2>现在是 {new Date().toLocaleTimeString()}.</h2>
            </div>
           );

           ReactDOM.render(el,document.getElementById('app'));
       }

    //    setInterval(() => {
    //     const el = (
    //         <div>
    //         <h1>Hello, world!</h1>
    //         <h2>现在是 {new Date().toLocaleTimeString()}.</h2>
    //         </div>
    //        );

    //        ReactDOM.render(el,document.getElementById('app'));
    //    }, 1000);
    setInterval(tick, 1000);
    </script>
</body>
</html>